Using Services in FLReconstruct Modules

Introduction

If you have just started using Falaise or the FLReconstruct application, we strongly recommend that you familiarize yourself with the basic usage of FLReconstruct covered in The FLReconstruct Application. You should also be familiar with composing and using pipeline modules, as covered in Writing FLReconstruct Modules.

In FLReconstruct, modules are the basic "unit" for processing events. Each event stores data relevant to that event, but creation, use, and interpretation of this data may require other data which common to a set of events (e.g. a detector run). These data are supplied through Services.

Your module can access any services it needs via the datatools::service_manager reference supplied to its constructor by the flreconstruct application. From this, you can get a smart pointer to a current service.

In this tutorial, we will see how to implement a module requiring the snemo::geometry_svc service.

Implementing a Service-Aware Module

Source Code for Service-Awareness

This tutorial builds on the basic module implemented in Writing FLReconstruct Modules. You should therefore have a workspace and module sources arranged as

$ cd MyWorkspace
$ ls
MyModule
$ cd MyModule
$ ls
CMakeLists.txt         MyModulePipeline.conf
MyModule.cpp           MyModulePipeline2.conf
$

The CMakeLists.txt build script and .conf pipeline scripts are identical to the earlier tutorial. We begin by modifying the module's implementation as follows:

// Interface from Falaise
#include "falaise/snemo/processing/module.h"

#include "falaise/snemo/services/geometry.h"

class MyModule {
 public:
  // Default constructor
  MyModule() = default;

  // User-defined Constructor
  MyModule(falaise::config::property_set const& /*ps*/, datatools::service_manager& sp)
      : geosvc{sp} {}

  // Process event
  falaise::processing::status process(datatools::things& /*e*/) {
    std::cout << "MyModule::process called!\n";
    geosvc->tree_dump(std::cout);
    return falaise::processing::status::PROCESS_OK;
  }

 private:
  snemo::service_handle<snemo::geometry_svc> geosvc;
};

// Register module with Falaise's plugin system on load
FALAISE_REGISTER_MODULE(MyModule)

The changes are pretty simple:

1. The service is held as a data member of type snemo::service_handle<snemo::geometry_svc>
   • snemo::service_handle is the "smart pointer" holding the service implementation
   • snemo::geometry_svc is the type of the service implementation we need.
2. The service is initialized by in MyModule's constructor from the supplied datatools::service_manager instance.
3. The service is used in the process member function, here for illustration only by calling the tree_dump member function of the held snemo::geometry_svc instance.

You do not need to worry about checking that the service is correctly constructed and valid. snemo::service_handle will throw exceptions if:

• A valid service of the requested type cannot be constructed
• The service is accessed (e.g. geosvc->tree_dump(std::cout)) and is not valid

The flreconstruct pipeline with handle these errors and report them on the command line.

Building and Running a Service-Aware Module

No special steps are needed to build or run a service-aware module, so you can follow the build instructions from the original example and run the module in the same way.

Available Services

• snemo::geometry_svc : queries related to geometric positions, etc in the detector